Whether you’re trying to finagle the truth from a teenager or you suspect a friend is fabricating a story, catching someone in a lie takes a bit of effort. Scientific American took a look at military interrogation tactics to see what works in everyday life and found asking left-field questions is a good way to trip up a liar.

When someone’s lying they usually have the story fully rehearsed and ready to go. So, to figure out if they making something up, it’s good to try and trip them up as they go. Scientific American explains:

People who are interrogated often know they are under suspicion, so they practice their answers ahead of time. In addition, liars are under high cognitive strain as they try to keep their story straight and at the same time act calm and collected. If you ask them something unexpected, they often stumble when put on the spot—enabling you to catch them in a lie.

When someone’s telling you a story you suspect is false, keep them on their toes by asking weird questions as you talk with them. Specifics are good here and the more unrelated to lie they’re telling the better. For example, if you think someone’s lying about being at a movie theater, ask them what the previews were, or if a particular B-list actor was in the movie. Head over to Scientific American for a bunch more ways to catch a liar.